In machining of metal materials so-called difficult-to-cut materials such as heat resistant alloys and high hardness materials (hereinafter simply referred to as machining of difficult-to-cut materials), a cutting insert having a cutting edge that is arcuate in plan view, such as that disclosed in International Publication No. 2010/023659, is used. Such a cutting insert is advantageous in machining of difficult-to-cut materials compared to the case of a cutting edge that is linear in plan view, from the viewpoint that generated chips are thin and that the cutting edge strength is high.
However, generated chips become thicker with the increase in depth of cut, and therefore, even when the cutting insert described above is used, cutting resistance may increase and the cutting edge may become liable to fracture.
PTL 1: International Publication No. 2010/023659